This invention relates to the conditioning of water bodies such as lakes, reservoirs and ponds and more particularly relates to the conditioning of such water bodies by manipulation of the thermal/density structure and oxygen content thereof.
Deep water bodies typically develop three characteristic layers due to the absorption of heat and the resulting differences in temperature and density from the surface downward. The upper or surface layer is a relatively warm mixed layer referred to as the "epilimnion". The epilimnion is the layer in which algal and weed growth becomes a problem in lakes and reservoirs. The metalimnion layer is located below the epilimnion and is characterized by rapid decreases in temperature and increases in density with depth. The temperature change in the metalimnion layer is generally greater than one degree centigrade per one meter depth increment. The depth within the metalimnion where temperature and density change is greatest per depth increment is called the "thermocline". Below the metalimnion is the uniformly cold layer called the "hypolimnion".
Being at the surface of the water body, the epilimnion layer has contact with the atmosphere and the attendant atmospheric gas exchange causes the warmer epilimnion layer to absorb oxygen. The lower layers are however isolated from the atmospheric gas exchange by the thermal/density stratification of the water body. Because of this thermal/density isolation from atmospheric gas exchange and both aerobic and anaerobic decomposition, the hypolimnion, metalimnion, and occasionally the lower epilimnion become devoid of oxygen and accumulate high concentrations of nutrients (i.e., nitrogen and phosphorus), carbon dioxide, and chemically reduced compounds such as manganese, iron, and sulfide. This accumulation often results in water quality problems for recreational use, water supply use, and aquatic habitat.
Accordingly, it is an object of the present invention to provide a new and improved apparatus and method for conditioning water bodies to alleviate water quality problems caused by deleterious accumulations of the type mentioned hereinbefore.
Another object of the invention is to provide a new and improved apparatus and method for manipulating or altering the thermal structure and metabolic/oxygen status of a water body to maintain or improve water quality.
A further object of the invention is to provide an apparatus and method for altering the thermal structure of a water body by creating or inducing new oxygenated, isothermal layers at various preselected depths in the water body.
A still further object of the invention is to provide an apparatus and method for redistributing oxygen available in a water body and introducing additional oxygen to one or more induced isothermal layers.
A still further object of the invention is to provide an apparatus and method for mixing water from different thermal layers in the water body and creating an oxygenated isothermal layer which will induce beneficial chemical reactions such as the precipitation of phosphorus and particulate matter.
Yet another object of the present invention is to provide an apparatus and method for creating multiple depths of steep temperature and density gradients ("thermoclines") to act as barriers to upward diffusive transport of nutrients and other bottom generated constituents such as iron, manganese, carbon dioxide, hydrogen sulfide and dissolved organic compounds.
Still another object of the invention is to provide an apparatus and method for aerating and circulating a selected depth interval of a water body.
Other objects will be in part obvious and in part pointed out more in detail hereinafter.
It has been found that the foregoing and related objects and advantages are attained in an apparatus for conditioning stratified water bodies comprising a reservoir and at least one upwelling and one return conduit adapted for generally vertical disposition within the water body and having an upper end fluidly connected to the reservoir. Each conduit has a plurality of ports longitudinally spaced along the conduit for fluidly connecting the conduit to the water body. These ports are spaced so as to afford fluid communication with predetermined depth levels of the epilimnion, metalimnion, and hypolimnion layers of the water body. Flow control assemblies are provided at each port for selectively alternately opening and closing off the ports to permit selective fluid communication with the predetermined depth levels. A pumping apparatus is connected to the upwelling conduit for moving water from the water body through the selected open inlet ports of the upwelling conduit through the upwelling conduit to the reservoir and through the return conduit from the reservoir for discharge out of the selected open discharge ports of the return conduit into the water body. In a specific embodiment of the invention, the reservoir is submerged below the surface of the water body and has an upper wall forming an interior gas chamber so as to define a gas-liquid interface within the chamber when submerged within a water body.
The new and improved method of the present invention for manipulating the thermal/density structure and oxygen content of a water body with a water circulating apparatus having upwelling and return conduits extending through the epilimnion, metalimnion and hypolimnion layers comprises selectively drawing water from at least one of any of said layers through the upwelling conduit. At least one new inducted isotherm is formed at a selected depth within the layers by controllably injecting the drawn water from the return conduit into the water body at the selected depth to form a barrier to upward diffusive transport of nutrients.